1. Description of the Prior Art
The invention relates to a device for evaporation of liquefied natural gas (LNG), which device via pipes is connected to a vessel moored by means of anchor chains, comprising at least one pipe through which LNG flows, the outside of said pipe may be brought in contact with sea water as a heating medium.
Seawater-heated vaporisers, located on shore, are presently in use on land-based LNG receiving terminals, where the vaporised gas, hereafter referred to as NG is transported to consumer via the pipeline system.
Such receiving terminals may comprise insulated tanks for receiving LNG from the vessel, a vaporiser or heat exchanger for vaporisation of LNG, and a control -and metering module for adjustment and metering of the gas which is passed to the consumer pipelines.
The known vaporiser comprises pipes, which are sprinkled with seawater. The heat energy of the seawater is transferred to the LNG located inside the pipe, which causes heating of the LNG that in turn leads to evaporation and superheating of the LNG towards ambient temperature. The difference in temperature between LNG and vaporised/superheated gas is approximately 170-180xc2x0 C. Maximum energy transfer from the seawater corresponds to a temperature reduction of 5-8xc2x0 C. The flow rate of circulating seawater therefore has to be significantly larger than the flow rate of LNG/NG, which is vaporised and superheated. The seawater is taken from the sea in the vicinity of the terminal and is returned to an area as far from the inlet as necessary to prevent mixing and short-circuiting.
Several disadvantages are related to the known vaporiser.
Due to the small temperature difference available, the seawater volume has to be disproportionally large. This leads to high power requirements to run the circulation pumps and therefore to a low energy efficient process.
Long inlet and outlet pipes with large diameters are required for supply and return of the seawater to a location at large depth in the sea in order to prevent detrimental environmental consequences for the shore zone. This increases the requirement for large pumps and results in long pipelines.
In addition, strainers and devices for prevention of clogging and fouling inside the pipes are required.
To protect the seashore long pipelines with large diameters are also required onshore.
Devices of the known type therefore occupy a large area and are expensive to install and operate.
JP-A-11,148,599 describes a device suitable for evaporation of liquefied natural gas (LNG) connected to a vessel moored by means of anchor chains, comprising at least one pipe through which LNG flows, the outside of said pipe may be brought in contact with seawater as a heating medium, the pipe is immersed in the sea and connected to the vessel, and the pipe is enclosed by a tubular shell through which the seawater is pumped by means of a propeller which is operated by a motor installed on board the vessel.
The objective of the invention is to provide a device of the above-mentioned type, but which does not include the mentioned disadvantages, and which should also contribute in holding mooring cables tight and straight.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The objective of the invention is fulfilled by a device according to claim 1.